1. Field of the Invention
This invention relates to a process for removal of hydrogen sulfide from a hydrogen sulfide-containing gaseous stream.
2. Description of Prior Art
Conventional liquid redox sulfur recovery processes use a redox couple dissolved in a solvent, normally water, to scrub hydrogen sulfide from a gas stream and convert it to sulfur. The redox agent is reduced by the hydrogen sulfide and regenerated by contacting with air in a separate vessel. For example, U.S. Pat. No. 3,068,065 teaches a process for the removal of hydrogen sulfide from gases in which the gases are washed with an aqueous solution of iron complexed with a polyamino polycarboxylic acid, the iron being in the ferric state for gas washing, and the aqueous solution, after contact with the gas, is regenerated by aeration. U.S. Pat. No. 4,009,251 teaches a process for removing hydrogen sulfide from gaseous streams in which the hydrogen sulfide is oxidized catalytically to sulfur in the presence of an aqueous chelate catalyst solution and a soluble alkaline metal or alkaline earth metal or ammonium or amine salt. U.S. Pat. No. 4,332,781 teaches the removal of hydrogen sulfide and carbonyl sulfide from sour gaseous streams in a staged procedure in which the sour gaseous stream is contacted with an aqueous reactant solution comprising an oxidizing reactant which converts the hydrogen sulfide to sulfur. The reduced aqueous reactants solution is then regenerated for reuse. Similar processes employing aqueous reactant solutions for removal of hydrogen sulfide from sour gas streams are taught by U.S. Pat. No. 4,390,516, U.S. Pat. No. 4,409,199, U.S. Pat. No. 4,359,450, U.S. Pat. No. 4,382,918, U.S. Pat. No. 4,388,293, U.S. Pat. No. 4,400,368, U.S. Pat. No. 4,518,576, and U.S. Pat. No. 4,091,073.
One of the main problems associated with conventional liquid redox sulfur recovery processes is dealing with the solid sulfur which is formed and which can plug the absorber or other vessel through which it passes and which is generally hard to separate and handle when formed from aqueous solutions.
The use of an absorbent to remove hydrogen sulfide from a gas stream containing hydrogen sulfide and carbon dioxide (CO.sub.2) and/or carbonyl sulfide (COS) is taught by U.S. Pat. No. 4,091,073; U.S. Pat. No. 4,388,293; U.S. Pat. No. 4,400,368; U.S. Pat. No. 4,382,918; U.S. Pat. No. 4,359,450; U.S. Pat. No. 4,409,199; and U.S. Pat. No. 4,332,781. The '199 patent teaches the use of an aqueous absorbent to absorb the bulk of the H.sub.2 S. In addition, H.sub.2 S absorbed by the aqueous absorbent is merely desorbed in a regeneration system to enable recycle of the aqueous absorbent to the absorber. Similarly, each of the '781 and '450 patents teaches absorption of H.sub.2 S followed by desorption and treatment of the desorbed H.sub.2 S with an aqueous reactant solution. The '293 patent, the '368 patent, and the '918 patent all teach a process for the removal of hydrogen sulfide and carbon dioxide from a gas stream in which the gas stream is contacted with an aqueous solution of a specific reactant ligand or chelate in a CO.sub.2 -selective absorbent containing specific stabilizers for improvement of chelate life. The hydrogen sulfide which may also be absorbed is immediately converted to sulfur by the reactant chelate, resulting in reduction of the reactant chelate. Finally, U.S. Pat. No. 4,091,073 teaches the use of an absorbent mixture of organic solvent and aqueous reactant solution for simultaneous removal of hydrogen sulfide and carbon dioxide from a variety of gas streams where the absorbent is used to absorb only CO.sub.2. The hydrogen sulfide in the gas stream is converted to sulfur.
In each of the U.S. patents discussed hereinabove in which a mixture of an aqueous reactant solution and an absorbent are employed for removing hydrogen sulfide from a gas stream, reaction of the aqueous reactant solution with the hydrogen sulfide is carried out in the absorber thus creating a likelihood of absorber plugging due to the formation of sulfur therein. In addition, such processes require the transport of sulfur from the absorber vessel to other processing vessels for further treatment and/or separation.